Hedge fund billionaire Ken Griffin could be about to lose a chunk of his estimated $5.5 billion fortune.

On Wednesday, the founder of Citadel LLC, the largest hedge fund in Chicago, filed for divorce from his wife of 11 years, Anne Dias-Griffin, the founder of hedge fund Aragon Global Management.

The situation is acrimonious after Ken, the world’s 270th-richest man, filed while Anne was taking their three kids, ages 6, 3 and 2, on vacation to London.

A source said, “She was blindsided.”

Anne has hired famously ferocious divorce attorney Robert S. Cohen, who said in a stern statement, “Ken Griffin unilaterally filed a divorce petition today with no notice to either me or my client, knowing full well that she had just left for summer vacation with their three young children and would therefore be unable to respond. Anne’s highest priority remains her family, especially the well-being of her children.”

A source said Ken and Anne had been negotiating for months, but couldn’t reach an agreement: “They have been separated for more than a year, the matter came to a head, and he filed for divorce.”

The couple has a prenup which sources say allows Anne a cash sum for their years of marriage, but does not cover their real estate portfolio and art collection.

A lawyer for Ken said, “This is a personal matter and the family asks for privacy as they work through this process.”

But, given their vast wealth and profile in Chicago, the divorce is certain to attract more attention.

Another source summed up, “This could be one of the biggest divorce cases to go to litigation in US history.”